Re: Faraday induction

[Eugene Mosca <emosca@PTD.NET>]

On 5/31/01 1:35 PM, "John S. Denker" <jsd@MONMOUTH.COM> wrote:

> At 09:51 AM 5/31/01 -0400, Eugene Mosca wrote:
> > Is there a conventional definition of voltage?  If so, what is it?
>
> How about energy per unit charge?

Does this mean that the kinetic energy per unit charge of charged particle
in an beam passing through a surface is voltage?

> > Is the definition valid in a region where there is both a rotational and an
> > irrotational electric field?
>
> Yes, but in the presence of non-potential voltages, you can't speak of the
> voltage difference between point A and point B without specifying the path
> that the test charge takes from A to B.

In the example given of the cut conducting ring in an increasing magnetic
field, inside the material of the conductor the tangential (azimuthal
component of the net electric field is everywhere zero.  Thus, for a path
staying within the conductor from one side of the cut to the other the
voltage difference is zero.  Correct?

> > Does the voltage of a battery differ from the
> > terminal potential difference?
>
> It does not differ in ordinary situations, such as situations where
> Kirchhoff's laws apply.

The terminal potential difference V is equal to the emf - Ir, where r is
the internal difference and I is the current.  The voltage between the
terminals is also equal to the emf ­ Ir, but we cannot write  this without
using the term emf, or can we?  How is this relation expressed without using
the emf word?

> OTOH if the battery is a region of changing magnetic fields, all bets are
> off, as discussed above.  There is no "terminal potential difference" and
> one would have to work pretty hard to define a nitpick-resistant definition
> of "the" voltage of the battery.

It seems to me the terminal potential difference is just the negative of the
line integral of the irrational part of the electric field from one terminal
to the other.



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